The action of LH on ovarian steroidogenesis is not completely understood. However, mitochondria must be target organelles of the overall LH response since they are the exclusive site for pregnenolone systhesis, the rate limiting step of steroidogenesis. We showed that mitochondrial steriodogenesis is increased by acute LH treatment of follicles. At the biochemical level, this LH-stimulated increase in pregnenolone synthesis is accompanied by activation of mitochondrial cyclic AMP-dependent protein kinase, phosphorylation of specific mitochondrial proteins, and increased 32p incorporation into mitochondrial phospholipids. Furthermore, isolated ovarian mitochondria by themselves can phosphorylate specific mitochondrial proteins, as well as incorporate 32pi into phospholipids. Since phosphorylation is a major means of post-translational requlation of enzyme activity, and because recent studies indicate that phospholipids may regulate mitochondrial steroidogenesis, we propose to study protein phosphorylation and phospholipid metabolism in mitochondria of medium follicles from porcine ovaries. Other laboratories have investigated the role of protein phosphorylation or phospholipids in the regulation of steroidogenesis using cytosolic preparations. However, since stimulation of mitochondrial pregnenolone synthesis is one of the earliest effects of LH on the ovary, it is logical that studies should also be done on mitochondria. Medium follicles will be incubated with LH and changes in mitochondrial protein phosphorylation and phospholipid metabolism will be studied. Also experiments on isolated ovarian mitochondria will be done. Changes in mitochondrial function and structure associated with mitochondrial protein phosphorylation and phospholipid metabolism will be determined. These studies will enhance our knowledge of LH action on the ovary, and information derived from these experiments may be useful in the treatment of ovarian disorders and in the regulation of ovarian function.